Pattern-matching Conditions

The pattern-matching conditions compare character data.

LIKE Condition

The LIKE conditions specify a test involving pattern matching. Whereas the equality operator (=) exactly matches one character value to another, the LIKE conditions match a portion of one character value to another by searching the first value for the pattern specified by the second. LIKE calculates strings using characters as defined by the input character set. LIKEC uses Unicode complete characters. LIKE2 uses UCS2 code points. LIKE4 uses UCS4 code points.

char1 is a character expression, such as a character column, called the search value.

char2 is a character expression, usually a literal, called the pattern.

esc_char is a character expression, usually a literal, called the escape character.

The LIKE condition is the best choice in almost all situations. Use the following guidelines to determine whether any of the variations would be helpful in your environment:

Use LIKE2 to process strings using UCS-2 semantics. LIKE2 treats a Unicode supplementary character as two characters.

Use LIKE4 to process strings using UCS-4 semantics. LIKE4 treats a Unicode supplementary character as one character.

Use LIKEC to process strings using Unicode complete character semantics. LIKEC treats a composite character as one character.

If esc_char is not specified, then there is no default escape character. If any of char1, char2, or esc_char is null, then the result is unknown. Otherwise, the escape character, if specified, must be a character string of length 1.

All of the character expressions (char1, char2, and esc_char) can be of any of the data types CHAR, VARCHAR2, NCHAR, or NVARCHAR2. If they differ, then Oracle converts all of them to the data type of char1.

The pattern can contain special pattern-matching characters:

An underscore (_) in the pattern matches exactly one character (as opposed to one byte in a multibyte character set) in the value.

A percent sign (%) in the pattern can match zero or more characters (as opposed to bytes in a multibyte character set) in the value. The pattern '%' cannot match a null.

You can include the actual characters % or _ in the pattern by using the ESCAPE clause, which identifies the escape character. If the escape character precedes the character % or _ in the pattern, then Oracle interprets this character literally in the pattern rather than as a special pattern-matching character. You can also search for the escape character itself by repeating it. For example, if @ is the escape character, then you can use @@ to search for @.

Note:

Only ASCII-equivalent underscore (_) and percent (%) characters are recognized as pattern-matching characters. Their full-width variants, present in East Asian character sets and in Unicode, are treated as normal characters.

TRUE if x does [not] match the pattern y. Within y, the character % matches any string of zero or more characters except null. The character _ matches any single character. Any character can follow ESCAPE except percent (%) and underbar (_). A wildcard character is treated as a literal if preceded by the escape character.

SELECT last_name
FROM employees
WHERE last_name
LIKE '%A\_B%' ESCAPE '\'
ORDER BY last_name;

To process the LIKE conditions, Oracle divides the pattern into subpatterns consisting of one or two characters each. The two-character subpatterns begin with the escape character and the other character is %, or _, or the escape character.

Let P1, P2, ..., Pn be these subpatterns. The like condition is true if there is a way to partition the search value into substrings S1, S2, ..., Sn so that for all i between 1 and n:

If Pi is _, then Si is a single character.

If Pi is %, then Si is any string.

If Pi is two characters beginning with an escape character, then Si is the second character of Pi.

Otherwise, Pi = Si.

With the LIKE conditions, you can compare a value to a pattern rather than to a constant. The pattern must appear after the LIKE keyword. For example, you can issue the following query to find the salaries of all employees with names beginning with R:

SELECT salary
FROM employees
WHERE last_name LIKE 'R%'
ORDER BY salary;

The following query uses the = operator, rather than the LIKE condition, to find the salaries of all employees with the name 'R%':

SELECT salary
FROM employees
WHERE last_name = 'R%'
ORDER BY salary;

The following query finds the salaries of all employees with the name 'SM%'. Oracle interprets 'SM%' as a text literal, rather than as a pattern, because it precedes the LIKE keyword:

SELECT salary
FROM employees
WHERE 'SM%' LIKE last_name
ORDER BY salary;

Case Sensitivity

Case is significant in all conditions comparing character expressions that use the LIKE condition and the equality (=) operators. You can perform case or accent insensitive LIKE searches by setting the NLS_SORT and the NLS_COMP session parameters.

When you use LIKE to search an indexed column for a pattern, Oracle can use the index to improve performance of a query if the leading character in the pattern is not % or _. In this case, Oracle can scan the index by this leading character. If the first character in the pattern is % or _, then the index cannot improve performance because Oracle cannot scan the index.

LIKE Condition: General Examples

This condition is true for all last_name values beginning with Ma:

last_name LIKE 'Ma%'

All of these last_name values make the condition true:

Mallin, Markle, Marlow, Marvins, Mavris, Matos

Case is significant, so last_name values beginning with MA, ma, and mA make the condition false.

Consider this condition:

last_name LIKE 'SMITH_'

This condition is true for these last_name values:

SMITHE, SMITHY, SMITHS

This condition is false for SMITH because the special underscore character (_) must match exactly one character of the last_name value.

ESCAPE Clause ExampleThe following example searches for employees with the pattern A_B in their name:

SELECT last_name
FROM employees
WHERE last_name LIKE '%A\_B%' ESCAPE '\'
ORDER BY last_name;

The ESCAPE clause identifies the backslash (\) as the escape character. In the pattern, the escape character precedes the underscore (_). This causes Oracle to interpret the underscore literally, rather than as a special pattern matching character.

Patterns Without % ExampleIf a pattern does not contain the % character, then the condition can be true only if both operands have the same length. Consider the definition of this table and the values inserted into it:

Because Oracle blank-pads CHAR values, the value of f is blank-padded to 6 bytes. v is not blank-padded and has length 4.

REGEXP_LIKE Condition

REGEXP_LIKE is similar to the LIKE condition, except REGEXP_LIKE performs regular expression matching instead of the simple pattern matching performed by LIKE. This condition evaluates strings using characters as defined by the input character set.

source_char is a character expression that serves as the search value. It is commonly a character column and can be of any of the data types CHAR, VARCHAR2, NCHAR, NVARCHAR2, CLOB, or NCLOB.

pattern is the regular expression. It is usually a text literal and can be of any of the data types CHAR, VARCHAR2, NCHAR, or NVARCHAR2. It can contain up to 512 bytes. If the data type of pattern is different from the data type of source_char, Oracle converts pattern to the data type of source_char. For a listing of the operators you can specify in pattern, refer to Appendix D, "Oracle Regular Expression Support".

match_parameter is a text literal that lets you change the default matching behavior of the function. You can specify one or more of the following values for match_parameter:

'i' specifies case-insensitive matching.

'c' specifies case-sensitive matching.

'n' allows the period (.), which is the match-any-character wildcard character, to match the newline character. If you omit this parameter, then the period does not match the newline character.

'm' treats the source string as multiple lines. Oracle interprets ^ and $ as the start and end, respectively, of any line anywhere in the source string, rather than only at the start or end of the entire source string. If you omit this parameter, then Oracle treats the source string as a single line.

If you specify multiple contradictory values, then Oracle uses the last value. For example, if you specify 'ic', then Oracle uses case-sensitive matching. If you specify a character other than those shown above, then Oracle returns an error.

If you omit match_parameter, then:

The default case sensitivity is determined by the value of the NLS_SORT parameter.